enter image description here I have issues with dirty water in filter area and dishes not coming clean. This is a new dishwasher. Old one had similar issues so I think it is the drain and not dishwasher. Is the drain setup ok? Would it be better going to disposal? There is no possibility of adding an air gap.

Update: The upright pipe is what I think is an attempt at a loop..air gap thing. The plastic drain hose from the dishwasher comes out of the dishwasher..across the bottom of the cabinet. Up the side of that white pipe where it becomes clamped to a copper pipe. That empties into the white pipe which goes back down to the bottom of the cabinet and out its own drain. Thanks!

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    Hello, and welcome to Stack Exchange. Some labels on that photo would be really helpful (e.g. is that corrugated plastic tube the dishwasher drain? what's the stack on the left with the visible printing?). Commented May 2, 2018 at 16:08
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    NOTE: If you abandon the standpipe, make sure you cap it off. If the standpipe is unused, the trap will dry out and allow sewer gases to enter the home.
    – Tester101
    Commented May 3, 2018 at 11:22
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    I usually bring the flex tube through the cabinet as high as I can that keeps dirty water from laying in tube
    – Kris
    Commented May 3, 2018 at 13:01
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    @kris It can't be serving as an air admittance device, since it has a trap. Right now it's serving as an air admittance device for the dishwasher drain. If you remove the dishwasher drain, it's no longer needed.
    – Tester101
    Commented May 3, 2018 at 15:01
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    Thanks for the excellent advice. I have connected it to the disposer with a high loop and capped off the standpipe...all for about $12. So far so good. Commented May 4, 2018 at 15:25

3 Answers 3


Put the dishwasher drain line into the disposal. But that is NOT your air gap. There is a difference between an air gap and a trap. The output of the disposal has a trap, which is important. But you also need to have an air gap. A trap prevents sewer gas from escaping through the drain. An air gap prevents sewer water from coming into the dishwasher if the drain pipe is clogged.

However, an air gap does not need to be the old style of funny looking metal/plastic thing on the corner of the sink. Instead, you can use a flexible hose from the dishwasher that loops up above the height of the sink drain, as far as possible to the underside of the counter and then loops down and into the disposal. This does not require anything visible above the counter or any cutting holes into the sink or counter.

Assuming the corrugated plastic tube is your dishwasher drain line, move the end to the disposal and attached the middle of it as high up under the counter as you can and you're all set.

Drawing showing dishwasher using loop as air gap

  • Technically, the "air gap" is provided by the disposer. The high loop in the dishwasher drain hose, is to prevent a backup in the sink from flooding out the dishwasher. Basically, the sink would have to be just about overflowing, before water would drain into the dishwasher.
    – Tester101
    Commented May 3, 2018 at 11:49
  • @Tester101 - I disagree. A disposer, in totally normal usage, can easily fill up with water past the level of the dishwasher drain tube, so it does not function as an air gap. An air gap is designed so that it would take extraordinary circumstances ("the sink would have to be just about overflowing") for water to flow backwards into the dishwasher. The disposer is required to have a trap to prevent sewer gases from escaping, and that same trap functions for the dishwasher connected to the disposer. But that trap is NOT an air gap. Commented May 3, 2018 at 14:03
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    An "Air Gap", is a way to equalize air pressure within a pipe. The disposer is open at the top, which allows the system to equalize the pressure. The high loop drain is not an air gap, it's a trap (sort of).
    – Tester101
    Commented May 3, 2018 at 14:59
  • @Tester101 I still disagree. It is NOT about equalizing pressure. I am sure there are situations where that is needed (and devices designed to do so). But an air gap is to prevent backflow by having a gap, which is in the air or filled with air. That can be totally open (like a faucet placed above a sink), a small fixture that specifically provides a gap (the traditional ugly thing on the corner of a sink connected to a dishwasher drain) or a high loop which effectively provides a gap because the drain water has to come all the up to the top and then back down... Commented May 3, 2018 at 15:19
  • so that in order for water to backflow it would have to fill up from the other direction, which will not happen except under the most extreme circumstances. My guess is that the high loop is permitted for a dishwasher because even in the extremely unlikely situation of that allowing a backflow into the dishwasher, several other things would have to fail simultaneously (e.g., the solenoid/valve controlling the water pipe going into the dishwasher) in order for there to be any backflow into the water main. Commented May 3, 2018 at 15:19

Put the dishwasher drain line into the disposer. The disposer internal cavity becomes your air gap.

There is a slug inside the disposer dishwasher connection that needs to be removed.

  • If you connect the dishwasher drain line to the disposer but don't rearrange it as an air gap then if the drain coming out of the disposer is clogged the overflow will go into the dishwasher instead of the sink which will (a) not necessarily be obvious and (b) really mess up the dishwasher. Commented May 2, 2018 at 20:35
  • Yes - I am wondering how that works but I see setups online where the dishwasher is connected to disposer without an air gap. Commented May 2, 2018 at 21:35
  • @SusanGentry The basic answer is "it doesn't work, unless you have either a traditional air gap or a hose loop as an air gap." Commented May 2, 2018 at 21:59
  • I have updated my picture to show how I think it is draining...with a standpipe and second drain. It also looks like I can't remove the joints to try to clean out the pipe. I'm wondering if the disposer method is superior to this standpipe setup. Commented May 2, 2018 at 22:01
  • The disposer method is superior for a bunch of reasons. Move the dishwasher hose and cap off the other drain. Commented May 3, 2018 at 2:25

It's possible that the drain line is just too long (developed length). I'd guess that somewhere in the installation instructions it says to only use the supplied drain hose, and not to extend it. This is because the length of the supplied drain hose was specifically chosen, based on the size of the discharge pump.

You don't show what's at the top of the copper pipe, but I'm guessing it's some type of U shaped pipe. So while it may seem like you've only extended the drain line a foot, or so. The bend at the end of the tube, could actually be like adding an additional foot or so. With this setup, you may have actually added two feet to the developed length of the drain. That may not seem like much, but it could be enough to cause poor draining.

Draining in to the disposer is definitely and option, and seems as though you should have enough drain hose length to do it. Just make sure you secure the drain hose in to the high loop configuration, that's described in other answers. Don't forget to make any modifications to the disposer, to allow it to accept the drain. And don't forget to cap the abandoned standpipe. Left unused, the trap will dry out, and allow sewer gas to enter the living space.

  • Thanks - this is so helpful. I think I will attempt the disposer solution and cap off the standpipe. I could always go back to the current solution if needed. Commented May 3, 2018 at 13:43

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